Lyme disease is a zoonosis caused by the tick-borne spirochaete B. burgdorferi (1). When a susceptible host is bitten by an ixodid tick, B. burgdorferi organisms enter the skin. In humans the initial skin manifestation is termed erythema chronicum migrans (ECM) whereas a long-standing infection of the skin produces acrodermatitis chronica atrophicans (2), The Borrelia organisms also enter the circulatory system of the host and are distributed to various organs, including the brain and joints (3). A secondary spread of the pathogens produces a variety of clinical syndromes, including lymphocytic meningoradiculitis (4), myocarditis (5) and chronic arthritis (6). In many patients the infection of some tissues, particularly the brain and joints, persists for years and can be severely disabling. These forms of chronic Lyme disease are a consequence of the host's inability to rid itself of the infectious agent and perhaps the development of an autoimmune reaction (7).
Diagnosis of Lyme disease has chiefly been based on clinical evidence. The best marker during the primary stage of infection has been the presence of erythema chronicum migrans (ECM) but these skin lesions may not always develop or they may manifest atypically (7). Moreover, Lyme disease can be confused with other illnesses characterized by neurologic or arthritic manifestations. When clinical histories are incomplete, serologic testing with determination of antibody titers is the best laboratory method of diagnosis. Indirect fluorescent antibody (IFC) staining tests and enzyme-linked immunosorbent assays (ELISA) are used to detect total immunoglobulins (8) or class-specific IgM and IgG antibodies to B. burgdorferi (9). ELISA is usually preferred because the procedures are more easily standardized and automated and because absorbance values can be statistically analyzed to give more objective results (8).
B. burgdorferi spirochaetes are helically shaped, motile cells with an outer cell membrane that surrounds a protoplasmic cylinder complex, consisting of the cytoplasm, the cell wall, the inner cell membrane and the flagella which are located not at the cell surface but in the periplasmic space between the outer cell membrane and the protoplasmic cylinder. The outer cell membrane and the flagella are assumed to play an important role in the host-parasite interactions during the disease and has been subjected to several investigations, identifying major surface-exposed proteins as important immunogens (11).
It has been shown that the earliest IgM antibodies formed against antigens of the B. burgdorferi strain B31, which was deposited in the American Type Culture Collection in 1983 with the accession number ATCC 35210, are directed against a genus-specific flagellar poly-peptide termed flagellin having a molecular weight of 41 kd (10) and which reacts with monoclonal antibody H9724 (22). IgG antibodies are also first directed to the 41 kd flagellin, but with advancing disease IgG antibodies form against other immunogens, especially against two abundant proteins with molecular weights of 31 kd and 34 kd. These two proteins, which have been denoted OspA (31 kd) and OspB (34 kd), have been found to be located at the B. burgdorferi surface and embedded in its outer fluid cell membrane (11). The OspA protein has been found to be less variable in its molecular weight and in its reactivity with monoclonal antibody H5332 (12), whereas the molecular weight of OspB proteins from different B. burgdorferi strains vary and the OspB proteins of different strains also show varying reactivity with two monoclonal antibodies against OspB (H6831 and H5TS (13). The main variation among OspA proteins is found between isolates from Europe and the United States.
Conventional diagnostic tests for Lyme disease have used whole spirochaetal sonic extracts as test antigens in ELISA to detect antibodies to B. burgdorferi, but this test yields unsatisfactory low diagnostic sensitivity (20 to 60%) during the early stage of infection (14), possibly due to a slow and late-appearing antibody response and to the inclusion of irrelevant cross-reacting antigens in the whole-cell preparations. In addition, the use of whole cells as test antigens may result in the occurrence of false positive reactions. For example, among patients with syphilis and in areas where a closely related relapsing fever Borrelia spp. co-exist with B. burgdorferi, serologic differentiation of Lyme disease from tick-borne relapsing fever is difficult (15). Detection of IgG antibody to B. burgdorferi in later stages of infection can help in distinguishing Lyme disease from aseptic meningitis, multiple sclerosis, serum negative rheumatoid arthritis, juvenile rheumatoid arthritis, and Reiter's syndrome (9).
Several researchers have focused on isolating flagellin or preparing flagellin-enriched whole cell or fractions for diagnostic agents so as to improve diagnostic tests for an early diagnosis of Lyme disease. For this purpose, Coleman et al. (15) have obtained B. burgdorferi fractions by treating whole spirochaetes with the denaturating detergent sodium dodecyl sulfate (SDS) so as to obtain a protoplasmic cylinder flagellar (PC) fraction which upon subsequent shearing, filtration and dialysis constituted a flagellin-enriched fraction from which immunogenic polypeptides (flagellin) were eluted and used as antigens in ELISA for IgG and IgM antibodies. The flagellin-enriched fraction was reported to be a useful antigen for early stage reactivity. Also, Grodzicki et al. (58) discloses fractions of B. burgdorferi containing flagellin.
Hansen et al. (16) describes a method of preparing purified preparation of flagella usable as an antigen in an ELISA analysis for IgM antibody detection.
U.S. Pat. No. 4,721,617 discloses the use of inactiviated whole B. burgdorferi spirochaetes as a vaccine against Lyme disease and broadly teaches the concept of using an outer envelope fraction or its component polypeptides in vaccines but does not distinguish or give guidance as to which components to select for this purpose.
EP 252 641 discloses the use of antibodies specific to one or more antigens of B. burgdorferi, e.g. related to the cell wall or cell membrane of the organism. OspA and OspB are mentioned as examples of such antigens and fractions of B. burgdorferi are mentioned in general. The antibodies are stated to be useful in detecting B. burgdorferi antigens in urine and in diagnosing Lyme disease.
As explained above, the enzyme-linked immunosorbent assays for the diagnosis of Lyme borreliosis have been based on whole cell preparations. Such ELISA methods have shown good sensitivity, but lacked specificity (8, 9 and 59). Other antigenic preparations have been used such as the flagellin and fractionated antigens containing flagellin (15 and 58). These tests have showed a sensitivity almost as good as the test based on whole cell antigens, and greater specificity. However, these latter tests have proved most useful in the diagnosis of early stages of Lyme disease. Flagellin or fractions containing flagellin has been shown to be less suitable for use in the diagnosis of later stages of Lyme disease, because of a low specificity, i.e. a high cross-reactivity with antibodies raised in connection with other related diseases. The specificity of an assay for B. burgdorferi antibodies of various stages of Lyme disease, in which assay flagellin or a flagellin-enriched fraction is used, could be too low to be generally usable. Thus, there is a need for developing an assay for use in the diagnosis of various stages of Lyme disease which assay has a high sensitivity and specificity for B. burgdorferi antigens.
Furthermore, it would be desirable to provide individuals such as humans and animals with a broad protection against Lyme disease by means of immunization. The present invention discloses easily extracted immunologically active B. burgdorferi fractions that increase the specificity of assays for B. burgdorferi antibody and are potential vaccine components and useful in antibody tests for the immunization and diagnosis of Lyme disease.